1. Field of the Invention
The present invention relates to a printing apparatus for printing an image provided on an original film onto a photosensitive film and, more particularly, to a printing apparatus for producing a color separation.
2. Description of the Background Arts
In a photoengraving process, it is necessary to prepare four color separations which contain information for each of the major printing colors: Yellow (Y), magenta (M), cyan (C) and black (BK). Each of the color separations is produced by printing an image provided on an original film onto a photosensitive film (unexposed film). Then, a reproduction process employing the four color separations is carried out, so that the color image corresponding to the original film is reproduced into a printing paper. When the printing paper is comprised of a plurality of color images such as pictures and characters, all of the images must be provided onto each of the color separations. The term "multiple printing" refers to the multiple operations for printing the images to be reproduced onto a photosensitive film for each color separation.
This multiple printing operation necessarily increases the number of films required for printing. Thus, the required films include the following:
a) four photosensitive films for respective color components Y, M, C and BK; PA1 b) original films for respective color components Y, M, C and BK each of which has a halftone negative original expressing an image such as pictures and characters; and PA1 c) a mask film.
Thus, the operation for performing multiple printing by successively combining these films in accordance with prescribed rules is extremely complicated and even a skilled operator requires a considerable time.
Further, since registration of the respective films must be performed with high accuracy in printing, it is necessary to align the positions of the films through register pins. In the multiple printing operation, the number of times for performing such registration is also considerably increased, thereby applying a heavy burden to the operator.
In order to cope with such situation, an apparatus for automatically performing printing operation has been developed. For example, Japanese Patent Laid-Open Gazette No. 60-10252 discloses an automatic printing apparatus in which a pallet group storing an original film and a photosensitive sheet (printing plate) is arranged at the back of an exposure plane of a printer. In the apparatus, one of the pallets selectively advances above the exposure plane while a suction plate of a carrier applying suction to a film in the pallet. Thus, the film is carried onto the exposure plane. The printing operation is automated by using this apparatus, to achieve a reduction in time for the printing operation as well as a reduction of the burden of the operator.
Since the films are generally large in size, the size of a pallet for storing the films must also be increased. Therefore, the aforementioned conventional automatic printing apparatus is considerably increased in plane size. Thus, not only is a wide area is required as an installation area for this automatic printing apparatus, but also it is not easy to correct problems which may arise in the central portion of the apparatus. Further, since a mechanism for moving each pallet must be provided in addition to a moving mechanism for moving a carrier for transfer of the film in the pallet onto the exposure plane, the mechanism for moving the respective parts is also complicated.